Extending G Suite with Add-ons

Add-ons are customized extensions of G Suite productivity applications such
as Gmail, Google Sheets, and Google Docs. Add-ons are built using
Apps Script—a rapid application development platform
based on JavaScript that lets you create business and productivity applications
quickly and easily.

Connect to non-Google services within G Suite applications, allowing you to
retrieve or upload data from those services into and from G Suite.

Create custom interfaces (sidebars, menus, and dialogs) that are displayed
within the G Suite application the add-on extends, potentially removing the
need for a user to switch browser tabs when working with multiple
applications.

You can create add-ons for your personal use, for use within your organization,
or publish them to the
G Suite Marketplace where millions of
users and domain administrators can find and install them.

Add-on types

Add-ons are defined by the application they extend (the host application).
There are two primary types of add-ons:
Gmail add-ons and Editor add-ons.